Chitosan

Chitosan is a natural chelating polymer obtained by deacetylation of chitin.Crabshells are the main sources of chitin because this latter can be found in big quantities. Chitin or chitosan can be also extracted from fungi or insects exoskeletons.

Structure  of Chitosan
(poly-b (1-4)-2-amino-2-deoxy-D-glucose)

Use of chitosan in water treatment

The high content of amino groups provide   to chitosan very interesting chelating properties versus heavy metals. These can be cations like Pb ²⁺ or Cu ²⁺ or anions like MoO₄^2-.

Although much work has been done about the sorption of heavy metals on chitosan, mechanism of adsorption is not well established for lot of them.

Chitosan can be prepared in different conditioning like gel beads, fibers or films.These preparations required to solubilized chitosan and acid acetic is largely used in this purpose.

Chitosan has a pKa about 6,2 and was partially soluble in dilute mineral acids such as HNO₃, HCl, H₃PO₄. This can be a problem in wastewater treatment process when chitosan is used for the recovery of metal ions from a acid media. The only acid mineral that seems to not solubilize chitosan is sulfuric acid. In order to improve  chemical and mechanical resistance of chitosan, a chemical reaction called crosslinking is necessary and can be carried out with glutaraldehyde or epichloridrin.